The Forbidden City has not accumulated water for 600 years? Journalist's on-site visit to the drainage system of the Forbidden City

On July 22nd, a sudden heavy rainfall caused some areas of the Palace Museum to accumulate water for a short period of time, becoming the focus of public attention. What is the real condition of the drainage system in the Forbidden City, which is over 600 years old? On July 31st, despite heavy rain in Beijing, the reporter conducted an on-site visit to the drainage system of the Forbidden City.

At 9 o'clock in the morning, the reporter arrived at Jinshui Bridge. The person in charge of the Palace Museum said that compared to defense and fire prevention, the main function of Jinshui Bridge is drainage.

It is reported that since ancient times, cities and ancient architectural complexes in Beijing have been designed with flood control and drainage systems, and the Forbidden City is no exception. At present, the Forbidden City has two independent drainage systems. Among them, the municipal sewage system of the Forbidden City was built in the 1950s to ensure the convenience of visitors after the Palace Museum opened to them. It was constructed after professional planning and design, and approval by higher authorities; However, rainwater drainage is still discharged into the Jinshui River using the ancient rainwater system.

The drainage system in front of the imperial palace hall of supreme harmony. Photo by Wang Jue

The relevant person in charge said that the rainwater drainage in the Forbidden City is a complex system. Courtyards are generally high in the middle and low on the upper side, with high in the north and low in the south. The water in the courtyard is directed into a hidden ditch or discharged into an open ditch on both sides of the courtyard through a money eye. When the open ditch encounters a platform or a building, a stone voucher hole is opened underneath it to allow water to flow through. The open ditch and hidden ditch communicate with various palaces and courtyards, and finally the water is directed into the Jinshui River and merged into the urban river channel. The drainage channels crisscross, just like the human circulatory system. The dry channels resemble the aorta, which can reach a height of over a person. The end of the drainage channels are as high as capillaries, ranging in height from 13 to 40 centimeters.

These canal systems were built in the Ming Dynasty and their engineering scale exceeded that of the Jinshui River on the ground. Both the Ming and Qing dynasties had regulations that required timely excavation and repair of palace ditches every year. For example, in the Qing dynasty, this work was mostly carried out in March each year. Throughout history, continuous dredging and maintenance have been necessary to maintain basic smoothness for 600 years.

At around 10 o'clock in the morning, it rained heavily, and the dragon head in front of the Taihe Hall in the Forbidden City began to spit water. The scene of "Nine Dragons spitting water" reappeared.

It is understood that currently, the rainwater drainage of the Forbidden City still uses the ancient rainwater system of the Forbidden City and is naturally discharged into the Jinshui River. The more accurate statement that the Forbidden City will not accumulate water in 600 years is that even if there is water, it can be quickly drained. To achieve this effect, on the one hand, it relies on the good ancient rainwater system of the Forbidden City, and on the other hand, the later cleaning and maintenance work is also an indispensable part of flood prevention.

The relevant person in charge of the administrative office of the Palace Museum introduced that during the design and construction of the Forbidden City, a complex and complete drainage system had already been designed, and both the Ming and Qing dynasties made strict regulations on timely cleaning, repairing, and maintaining drainage systems. However, it should be noted that in the design, construction, and maintenance of the drainage system in the Forbidden City, the main considerations are conventional silt such as roof ridge ash and dead branches and leaves. For these pollutants, rainwater flushing and daily cleaning can basically maintain the smoothness of the drainage network. In recent years, during our daily maintenance, we have found a large number of plastic bags, mineral water bottles, paper and other debris in the drainage system, and even found "large" items such as towels and clothing. These modern industrial products cannot be washed away by rainwater like mud and ash, but are often easily blocked at the corners of drainage ditches, the connection between branch ditches and underground ditches, and other narrow, difficult to detect and clean parts. Once a few points are blocked, it may often lead to some drainage facilities not working smoothly.

As for the ponding phenomenon in the Cining Palace, the person in charge of the World Heritage Monitoring Department of the Palace Museum said that the precipitation on July 22 was the first heavy rain that the Palace Museum has encountered since the beginning of summer this year. The 24-hour precipitation reached 93.5mm, close to the level of heavy rainstorm, of which the maximum hourly rainfall at 8:00 reached 50.4mm, reaching the level of rainstorm. We immediately activated the highest level emergency plan and conducted a carpet style inspection and investigation of all areas in the hospital, and dealt with any hidden dangers as soon as they were discovered.

The drainage system in front of the imperial palace hall of supreme harmony. Photo by Wang Jue

After inspection, there was a serious waterlogging in the open area, located on the west side of the Cining Palace courtyard. Due to heavy rainfall, the waterlogging reached 17 centimeters in a short period of time. We took measures such as manual drainage to completely drain the water 4 hours after the rain; 8 mild waterlogging areas, with a maximum depth of 6 centimeters, were completely drained within half an hour after the rain.

As the most well preserved ancient wooden palace complex in the world, the Palace Museum has always placed flood prevention work as a top priority in the protection of the Palace Museum's architecture and cultural relics since its establishment. A flood prevention working group has been specially established to prevent floods. In daily management, not only has an infrastructure pipeline information system been established, including drainage systems, but courtyard patrols are carried out in a timely manner after rain to record drainage blockage points. In addition, systematic drainage ditch inspections, dredging, and cleaning work are carried out every spring, summer, and autumn to ensure that the accumulated water in the Forbidden City can be discharged through the drainage system as soon as possible after heavy rain.

The Imperial Palace in the Rain. Photo by Wang Jue